Apogamy induction in Ceratopteris richardii

Two distinct generations, the sporophyte and the gametophyte, alternate to complete the life cycle of all land plants. The sporophyte generation undergoes meiosis to form spores, from which gametophytes develop. The gametophyte generation produces gametes, which undergo fertilization to produce the zygote, the first cell of the sporophyte, thus completing the life cycle. As a variation of this life cycle, some fern species can undergo apogamy and apospory, bypassing fertilization or meiosis, respectively, alternating from one generation to the other without changing chromosome number. Both apospory and apogamy occur in nature and can be induced in the laboratory. The apogamy process is particularly amenable to analysis at the molecular level because the sporophytes are generated directly from a single- layered, free- living gametophyte whose growing conditions can be easily manipulated and growth synchronized. Here, we report the successful induction of apogamy in the model fern Ceratopteris richardii by culturing gametophytes in the presence of high levels of exogenous sugars. We also have identified the minimum time developing C. richardii gametophytes require sugar to gain competence for apogamous production of sporophytes. At this time, no signs of sporophyte differentiation are detectable. These results establish an experimental system that will allow genes that are important in apogamy to be identified.